What happens when two processes on the same computer communicate via TCP?

If two processes communicate using a tcp socket, is it really tcp behind the scenes?

That is, is it limited by sender/receiver/congestion windows? Is there a slow start process? Does the data ever reach the OS'开发者_Go百科s tcp/ip stack?

Since it's obviously dependent on the operating system itself, I'm most interested with Windows' implementation. However, answers regarding other OS are also appreciated.

It does not depend if the two ends are managed by the same process but related to how do you refer one end from the other. If you're using localhost for hostname, it will reach the tcpip stack but not the adapter.

You can start from this link: Windows Sockets 2 Architecture

Windows Sockets are not limited to TCP, but a "tcp socket" is really TCP :)